Plasticizer refers to additives added to the material to increase the flexibility, fluidity, and plasticity of the material. Plasticizers are widely used material additives in industrial production. The use of plasticizers can improve the performance of materials, reduce production costs, and increase production efficiency. There are three theoretical explanations for the principle of action of plasticizers, namely lubrication theory, gel theory and free volume theory. Lubrication theory believes that plasticizer molecules play a role of lubrication between macromolecules, reducing the resistance between molecules, so that molecular chains can move freely. The gel theory believes that the macromolecular chains are in a "time-opening-time-closing" dynamic equilibrium under the action of the balance force, and the addition of plasticizer molecules makes the equilibrated molecular nodes solvate, allowing the macromolecular chains to continuously separate. Free volume theory believes that the plasticizer molecules are embedded between the molecular chains of the polymer, so that the free volume of the molecular chain increases, and the viscosity and glass transition temperature Tg decrease.
Figure 1. Three plasticizing theories
Due to the advantages of rich variety, excellent performance, simple synthesis process and environmental protection, plasticizers are commonly used as additives in the fields of plastic products, concrete, plaster, cement, gypsum, food packaging and cosmetics.
- Concrete: Generally speaking, high water content will make concrete fluidity and workability better. But when the concrete has enough water, the strength and water content of the concrete after setting are inversely proportional. Therefore, if the concrete is to have high strength, the amount of water in the concrete cannot be excessive, and the workability of the concrete will deteriorate at this time. Plasticizers can reduce the moisture content of concrete without affecting the workability of concrete, and at the same time increase the strength of concrete, so it is widely used in concrete.
- Gypsum drywall: The plasticizer used in gypsum drywall is also called dispersant. The role of the plasticizer in the drywall of the gypsum is to increase the workability before the gypsum sets. When preparing drywall of gypsum, it is usually necessary to dry the drywall by heating. In order to reduce the energy required to dry the dry wall, less water will be added during production. The result of adding water is to make the processability of gypsum worse, and adding plasticizer can improve its processability. In general, the amount of plasticizer added to the drywall of gypsum is very small. If excessive plasticizer is added, the retarding effect will occur, and the dry wall strength of gypsum will also become worse.
- Food packaging: Polylactic acid material has unique advantages as a food packaging material. When polylactic acid is used as a raw material to make food packaging materials, plasticizers are often needed to increase plasticity. Due to its strong solubility and good oil resistance, citrate plasticizers have become common plasticizers in the production of food packaging materials. Among them, tributyl citrate (TBC) and acetyl tributyl citrate (ATBC) are the two most commonly used citrate plasticizers. As the main plasticizer of PVC film for food packaging, citrate is especially suitable for the packaging of high fat content foods such as meat and the preservation of fungi and fresh vegetables. In addition, citrate plasticizers have the advantage of non-toxicity, so they are often used in pharmaceutical packaging materials.
Figure 2.Synthesis of tributyl citrate Structure of plasticizers TBC and ATBC
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